The invention relates generally to improvements in tools and more particularly to such tools having pivotal jaws or lever members. Tools of this type typically include hand-actuated devices such as pliers, grippers, spreaders, crimpers and the like. Such tools often include a pair of cross links pivotally attached to the jaws or attached to both the jaws and handles by pivot pins for imparting pivotal motion to the jaws in order to perform an operation on a workpiece. An example of such a tool is illustrated and described in U.S. Pat. No. 2,168,812.
Because each cross link in the above-described tools pivots on both of the jaws, they necessarily cross and slidably engage each other. As a result, one of the cross links in such previous tools is rotatably attached to its pivot pins in a plane that is offset relative to the plane of movement of the other cross link and to the plane of movement of the jaws. Because of such offset relationship, when the jaws engage a workpiece and a force is applied to the levers to perform the required operation, the reaction forces on the pivot pins cause an unbalanced bending moment in a plane perpendicular to the plane of motion of the jaws. Such reaction forces can also cause other undesirable effects such as stress concentrations at or about the cross link pivot pins and possible misalignment of the working surfaces of the jaws.
The present invention preferably includes at least one pair of linkage members pivotally interconnecting a pair of jaws or levers of a tool for spreading or closing the jaws in order to perform work on a workpiece. Each of the linkage members is pivotally attached to both jaws preferably by means of a pin member extending therethrough. Each linkage member includes apparatus for supporting and reinforcing the pin members of the other of the linkage members, thereby tending to balance the reaction forces imparted to the pin members as a result of the jaws acting on the workpiece.
The preferred supporting apparatus includes elongated openings in a portion of each linkage member for receiving therein the pin members of the other linkage member. The pin members move within the elongated openings as the jaws are pivoted and preferably engage the peripheral edges of the elongated openings at least when the jaws operatively engage the workpiece.
In one embodiment of the invention, at least one of the linkage members is integrally incorporated into one of the jaws or levers of the tool. Another preferred embodiment includes at least two pairs of linkage members preferably with an equal number of the linkage members being pivotally connected to each side of the jaws.